Create db-dao.md

暂未校对，基本上已经完成。
list markers are missing here. This will now render as 

MySQL MariaDB SQLite PostgreSQL CUBRID: version 9.1.0 or higher. Oracle MSSQL: version 2012 或更高版本，需使用 LIMIT/OFFSET。配置

instead of 

- MySQL
- MariaDB
- SQLite
...